1. Field of the Invention
This invention is in the field of internal combustion engines and, more specifically, such engines utilizing stratified fuel vapor air mixtures at the engine intake manifold. Both spark ignition and compression ignition internal combustion engines are included.
The following tentative classifications are taken from my related U.S. Pat. Nos. 4,147,137; 4,205,647; 4,425,892: 123/127, 32 ST, 32 SP, 122 D, 133, 190 A, 190 R, 430, 478, 523; 48/180 S; 261/89, 112.
2. Description of the Prior Art
A description of several prior art stratified air fuel mixtures and their use at engine intake is contained in reference A, U.S. Pat. 4,147,137, and this description material is incorporated herein by reference thereto. A brief summary of portions of this referenced subject matter particularly relevant to this patent application follows. Three types of intake air fuel mixture stratification are described therein: two barrel carburetor type; injected liquid spray type; multiregional type. Additionally, it is shown therein that stratification created at engine intake survives at least until combustion and that extremely lean air fuel ratio mixtures can be compression ignited. Further, it is shown therein that the noise consequent upon the compression igniting of near stoichiometric air fuel mixture regions can be reduced by making such regions individually of small volume, by scattering such regions about in amongst other kinds of regions, and by arranging that large differences exist in the compression ignition time delay characteristics of those regions which are compression ignited. The engine intake stratifier described and claimed in reference A creates a multiregional stratified air fuel mixture at engine intake by use of a stratifier valve with several separate air fuel mixture creating channels in combination with other elements. An engine intake mixture possessing multiregional stratification consists of many individual regions, each such region being small and essentially of uniform mixture within itself, and adjacent regions differ as to the air fuel ratio or the fuel type or both. The volume of individual regions in the multiregional air fuel mixture can be reduced by increasing the port indexing rate of the stratifier valve and the extent of scattering of one particular type of air fuel mixture region can be increased by increasing the number of active ports and separate air fuel mixture creating channels used by the stratifier valve. Differences in compression ignition time delay characteristics can be made larger by using different kinds of fuels and/or different air fuel mixture ratios as between the several separate air fuel mixture creating channels. In these ways the compression ignition noise level can be reduced when multiregional engine intake stratification is used as described in reference A.
It is a disadvantage of the engine intake stratifier of reference A that to accomplish large reductions of engine noise due to compression ignition requires the stratifier valve to become more complex mechanically, the number of separate air fuel mixing channels to become large, and the number of different fuels and hence fuel tanks to become large, and thus the complexity and cost of the engine system are increased as noise level is reduced.
Many of the beneficial objects made available by use of multiregional intake stratification result from the fact that compression ignition can then be used without excess engine noise. Because compression ignition is intended to occur, higher engine compression ratios are used with consequently increased engine efficiency. Additionally, engine supercharge can be used without excess engine noise. Because very lean and fully evaporated mixtures can be used, the exhaust emissions of undesirable smogforming materials and of smoke can be reduced as compared to conventional internal combustion engines. These and other beneficial objects made available by use of multiregional stratified engine intake mixtures are described in reference A.
Additional description of prior art stratified air fuel mixtures at engine intake and methods for creating such mixtures are contained in U.S. Pat. 4,205,647 and this description of prior art is incorporated herein by reference thereto.
The devices of this invention are used in combination with an internal combustion engine. The term "internal combustion engine" is used herein and in the claims to mean the known combination of elements comprising cylinders, cylinder heads, pistons operative within said cylinders and connected to a crankshaft via connecting rods, valves and valve actuating means or cylinder ports, lubricating system, cooling system, ignition system if needed, flywheels, starting system, fuel supply system, fuel-air mixing system, intake manifolds with inlets, and exhaust pipes, torque control system, etc. as necessary for the proper operation of said internal combustion engine. The term "internal combustion engine" is used hereinafter and in the claims to include also the known combination as described above but wherein the cylinders, cylinder heads, pistons operative within said cylinders and connected to a crankshaft via connecting rods, valves and valve actuating means or cylinder ports, are replaced by a rotary engine mechanism combination, comprising a housing with a cavity therein, and plates to enclose the cavity, a rotor operative with said cavity and sealing off separate compartments within said cavity and connecting directly or by gears to an output shaft, ports in said housing for intake and exhaust. The term "internal combustion engine" as used herein includes atmospherically aspirated internal combustion engines as well as supercharged engines using turbocharges or other types of intake air compressors. The term "internal combustion engine" is used herein and in the claims to mean internal combustion engines of the spark ignition type, of the compression ignition type and of the type using both spark and compression ignition.
The term, internal combustion engine mechanism, is used hereinafter and in the claims to mean all those portions of an internal combustion engine, as defined hereinabove, except the fuel air mixing system and the torque control system. An internal combustion engine mechanism contains an integral number of engine cylinders. These several cylinders can be connected in groups via an intake manifold common only to all cylinders of a group. Herein and in the claims each such group of engine cylinders connecting exclusively to a common intake manifold are considered to be a single internal combustion engine mechanism. Thusly defined two or more internal combustion engine mechanisms may be combined together in a single block and with a common crankshaft.
Continuously variable stratified fuel vapor air mixtures at engine intake are described in reference H, my U.S. Pat. No. 4,425,892 and differ from multiregional intake stratification and other prior art types of intake stratification. Continuously variable stratified air fuel vapor mixtures are created when, within a device for creating air fuel vapor mixtures for internal combustion engines from engine intake air flow and a moving evaporating liquid fuel, the intake air flows relative to the motion paths of the liquid fuel so that the air fuel vapor mixtures, created by the fractional evaporation of the moving multicomponent liquid fuel into adjacent intake air, change along the motion paths of the moving liquid fuel at least as to the fuel vapor fractions present and change across these liquid fuel motion paths at least as to the ratio of air to fuel vapor. Gradients of the compression ignition time delay can exist within a continuously variable stratified air fuel mixture. The compression ignition process can take place gradually where delay gradients exist and in consequence the engine noise of compression ignition is greatly reduced. Continuously variable stratification differs from multiregional stratification and from injected liquid spray stratification in that air fuel vapor ratio and/or the kinds of fuel molecules present vary in three dimensions at points throughout a continuously variable stratified mixture. A multiregional stratified mixture contains many differing regions but any one region is a volume of air fuel mixture within which both air fuel ratio and the kinds of fuel molecules present remain essentially the same in all three dimensions. In a similar way continuously variable stratification differs from injected liquid spray stratification as described, for example, in reference B. With these kinds of injected liquid spray stratification, the air fuel mixture formed by evaporation around each liquid droplet is approximately angularly symmetric about the droplet, except for flow distortions of the air-vapor envelope. Hence, within continuous surfaces, everywhere normal to radial lines from the droplet, with due allowances for envelope distortions, both the air fuel ratio and the kinds of fuel molecules present remain essentially the same in the two dimensions of the surface.
Reduced engine noise due to compression ignition can be achieved by use of continuously variable fuel air mixtures at engine intake. As discussed in reference A, compression ignition of air fuel mixtures occurs abruptly following a time delay interval and pressure waves are generated whose strength is proportional to the volume of air fuel mixture thus abruptly ignited. The engine noise of compression ignition results from these pressure waves and hence the engine noise is also proportional to the volume of air fuel mixture abruptly compression ignited. With multiregional stratification the noise of compression ignition can be reduced by reducing the volume of the individual regions and by creating differences in the compression ignition time delay between regions as described in reference A.
With continuously variable stratification the compression ignition time delay can also be made to vary continuously. The compression ignition time delay varies with the kinds of fuel molecules present as well as with the air fuel ratio. Air fuel mixtures that are stoichiometric or leaner in fuel content most commonly show increased compression ignition time delay with increasing air fuel ratio. The effects of the kinds of fuel molecules upon the compression ignition time delay are complex and can be very large. For example, pure benzene C.sub.6 H.sub.6 appears to have an almost infinite compression ignition time delay whereas normal hexane, C.sub.6 H.sub.14, has a very short compression ignition time delay. Additive fuel molecules, such as aromatic amines and organic peroxides, also greatly affect the compression ignition time delay as is well known in the art. The term delay gradient is here defined as the distance rate of change of compression ignition time delay along a line within an air fuel mixture. The delay gradients at any particular point in an air fuel mixture are a composite of the effects on compression ignition time delay of both the local variation of air fuel ratio and the local variation of kinds of fuel molecules present.
Within a continuously variable stratified air fuel mixture delay gradients can be created in three dimensions within the fuel containing portions of the mixture since the air fuel ratio and/or the kinds of fuel molecules present vary in three dimensions.
That compression ignition can take place in a gradual manner in the presence of a delay gradient can be seen by examining the known details and current theories of the compression ignition process of hydrocarbon fuels. Compression ignition takes place via a chain branching reaction between fuel and oxygen wherein reaction is carried onward by chain carriers, usually free radicals. Chain branching via creation of extra chain carriers, and hence reaction speed up, awaits the accumulation of some unknown chain branching intermediate, perhaps peroxide molecule, which is itself a product of the chain reaction. The compression ignition delay is thus the time needed to accumulate enough of this branching intermediate so that chain branching and reaction speed up can occur. Hence the concentration of chain carriers in a fuel air mixture remains low until the compression ignition time delay has almost expired since only then are large numbers of chain carriers being created via the branching intermediate. Once adequate branching commences chain carriers concentrations rise rapidly and the overall reaction accelerates rapidly and this speed up is compression ignition. Details of this hydrocarbon and oxygen chain branching reaction are presented in reference C and there is general agreement about these chemical characteristics of compression ignition even though many reaction details remain obscure.
Controversy, however, surrounds the description of the compression ignition process details following expiration of the delay period. According to the autoignition theory, as described for example in reference D, noisy compression ignition, such as knock, occurs only when the branching intermediate accumulates uniformly and thus the compression ignition delay expires essentially simultaneously throughout an appreciable volume of air fuel mixture. With a delay gradient the branching intermediate accumulates non-uniformly and ignition delay expires at different times in different places and the consequent autoignition must proceed gradually from one region to the next only as the ignition delay expires in each succeeding region, according to this autoignition theory.
According to the flame acceleration theory, as described for example in reference E, noisy compression ignition, such as knock, occurs when a slow moving normal flame meets a volume of air fuel mixture containing sufficient of the branching intermediate that compression ignition delay is about to expire throughout this volume. Since the normal flame is moved forward, at least in part, via the forward diffusion of chain carriers, a large speed up of the flame might well occur in a volume which was already generating chain carriers in large numbers via the branching intermediate, and this flame speed up is considered to be knock, or compression ignition, according to this theory. When, however, a slow moving normal flame enters a delay gradient, such flame speed up cannot occur since the needed amount of the branching intermediate can exist only in at most a very small volume. Hence, such a normal flame would advance only slowly through an air fuel mixture possessing a delay gradient, according to this flame acceleration theory.
According to the detonation wave theory, as described for example in reference F, the reaction acceleration consequent upon expiration of the ignition delay within one region generates shock waves emanating from this first reaction region and these shock waves can become detonation waves provided the shock compressed air fuel mixture immediately behind the wave front can also accelerate its own reaction sufficiently to reinforce the shock wave. If a detonation wave is thusly created, the compression ignition will be noisy according to this theory. The shock wave compressed air fuel mixture can only thusly accelerate its own reaction and create a detonation if the amount of the needed branching intermediate is already nearly adequate for expiration of the compression ignition delay. Though shock compression can speed up a reaction, it cannot appreciably increase the amount of the needed branching intermediate within the very short time of wave passage. Within the air fuel mixture possessing a delay gradient the initial shock wave creating reaction occurs in the region whose ignition delay interval first expires. In all adjacent regions the amount of branching intermediate is necessarily inadequate for expiration of the delay interval and hence is also inadequate for the reaction acceleration within the shock wave compressed material needed to create a detonation wave. A detonation wave and the consequent engine noise are thus not created when delay gradients exist, according to this detonation wave theory.
We thus see that the gradual and reasonably quiet occurrence of compression ignition will take place in air fuel mixtures possessing a delay gradient, according to each of the existing theories of compression ignition.